A stroke is called a cerebrovascular accident or CVA by medical professionals. It is usually caused by either:

Blockage of an artery in the brain by a blood clot or fatty deposits, which is called a cerebral infarction;

OR

A ruptured cerebral artery bleeding into the brain, which is called a cerebral hemorrhage.

Some strokes are caused by cerebral aneurysms.

The Social Security Administration sees large numbers of stroke cases.

Strokes Caused by Blockage of an Artery

Most strokes are caused by cerebral infarction in which an artery in the brain (see Figures 1 and 2 below) is blocked depriving the brain of blood and damaging brain tissue. An arterial thrombosis (blood clot) is the most common cause of cerebral infarction. Such a clot could form in a cerebral artery itself or in the heart as a result of a variety of heart problems and be pumped to the brain. Blockage of a cerebral artery by the fatty deposits of atherosclerosis can also deprive an area of the brain of blood and lead to infarction. Actually, many cerebral infarctions are caused by cerebrovascular disease in which a blood clot forms around fatty plaques. Unlike arteries in the heart or legs, cerebral arteries cannot be cleaned out of fatty blockages. However, if a stroke occurs as a result of a blood clot, brain damage can be lessened by clot-dissolving drugs. Medical attention must be sought within a few hours for treatment to be effective and clot-dissolving drugs pose some risk of causing deadly bleeding.

A piece of atherosclerotic plaque can break off inside one of the two internal carotid arteries in the neck, be pumped to the brain, and lodge in a cerebral artery to cause an infarction.

Figure 1: Veins of the brain.

Figure 2: Base of the brain, including main arteries.

Strokes Caused by Ruptured Cerebral Artery (Cerebral Hemorrhage)

The most frequent cause of hemorrhagic CVAs is uncontrolled hypertension (high blood pressure), often related to non-compliance with medical treatment. The Social Security Administration sees many such tragic cases. Bleeding in the brain may also occur from abnormal tangles of blood vessel growths called vascular malformations and cerebral aneurysms.

Strokes Caused by Cerebral Aneurysms

Incidence of Cerebral Aneurysms

A significant number of strokes are caused by cerebral aneurysms, which are enlarged, and weak areas of a cerebral artery that can rupture and cause a subarachnoid hemorrhage (SAH). Aneurysms in the cerebral circulation are common. They are estimated to occur in between 1% and 5% of the general population and account for 5% to 15% of strokes. The most common location for cerebral aneurysms is the anterior cerebral artery. Cerebral aneurysms are twice as common in women as in men. They occur more frequently in individuals with certain disorders such as autosomal dominant polycystic kidney disease. More than one aneurysm may be present.

Millions of Americans have cerebral aneurysms. Although somewhere between 50% to 80% of aneurysms are small and do not rupture—many are only found incidentally at autopsy—that still leaves millions of individuals at risk for death or debilitating stroke.

Effects of Rupture

If a stroke occurs, the prognosis is grave, with a mortality of about 40% to 50% within 30 days of the first rupture. For surviving patients with SAH, about 30% have significant neurological abnormalities. For instance, following SAH, 15% to 20% of individuals will develop hydrocephalus (fluid accumulation on the brain) and require further neurosurgical procedures to treat that serious brain disorder.

The following scale is widely used by physicians to describe a patient’s condition after SAH:

Re-bleeding Risk

If a person has experienced one rupture (bleeding episode) from an aneurysm, the risk of future bleeding is increased to 10 times that of someone with a no rupture history. If the aneurysm was large (10 mm or more), the risk of rebleeding is even higher.

If an aneurysm has not bled previously, data indicates a low bleeding risk of 0.05% per year; in aneurysms less than 7 mm, the 5-year risk approaches zero in the absence of a bleeding history. However, the size of an aneurysm is not the only consideration—aneurysms putting pressure on vital brain structures, such as a cranial nerve (see Figure 3 below), require surgical intervention at a smaller size.

Figure 3: Cranial nerves at the base of the brain.

Diagnosis and Surgical Treatment of Cerebral Aneurysms

Many unruptured cerebral aneurysms can now be identified with CTA or MRA, without the more invasive catheter angiography. However, catheter angiography better diagnoses SAH. Angiography of any type is not perfect and can fail to identify small aneurysms of less than 3 mm.

Cerebral aneurysms may be treated surgically to reduce the risk of rupture, rebleeding, or brain damage from pressure the aneurysm places on brain tissue. Surgery to place a metal clip on the neck of an aneurysm that connects it to a parent vessel has been the standard treatment in the past. This procedure is major brain surgery and requires a craniotomy. A piece of the skull (skull flap) is sawed under general anesthesia and laid back for entry into the brain. This surgery has risks and the surgical risks for small aneurysms considerably exceed the risks of conservative (non-surgical) treatment.

A second surgical option has been the use of detachable coils of various sizes and shapes, which can be inserted without opening the skull. These coils are advanced by microcatheter to the aneurysm through the femoral artery in the leg, and then up through the carotid artery in the neck into the cerebral circulation. The coil is then detached inside the aneurysm to block blood flow through the neck of the aneurysm into its main body. Thus, the patient is spared the very invasive craniotomy. Although the risk of rebleeding after coiling is slightly greater than after clipping, the safety of coiling appears greater in many instances. Medical judgment in individual cases is still required to determine the best treatment option, but it is likely that coiling will continue to replace a significant number of cases that would otherwise have required clipping.

Diagnosis of Stroke

Evidence that a CVA has occurred is based on history and physical examination, as well as neuroimaging with computerized tomographic angiography (CTA) or magnetic resonance angiography (MRA) of the brain. Cerebral catheter angiography, a much older procedure than CTA or MRA, is still sometimes used. It carries some risk and is not needed to evaluate most CVAs. Cerebral catheter angiography involves direct injection of x-ray contrast material to outline the arteries of the brain. A catheter is threaded through the femoral artery in the leg, up into a carotid artery in the neck, and then manipulated into the cerebral circulation where contrast injection takes place.

Recovery from Stroke

Brain cells that are killed by a stroke are not replaced with new cells. The brain cannot re-grow any part of itself. But it can re-arrange brain cell connections to some degree to compensate for injury. The ability of the brain to compensate for injury decreases with age. Recovery from stroke depends on the ability of remaining brain areas to perform necessary functions, and recovery of areas not permanently damaged by the CVA. Rehabilitation is very important in achieving maximum possible recovery, and should be instituted as soon as possible after the CVA.

Effects of Stoke

CVAs can be of all degrees of severity, and the type of damage they do depends on where in the brain they occur. Some CVAs cause death immediately, while others may cause little limitation. There might be good recovery, or very little.

Strokes can have many effects depending on what areas of the brain are damaged (see Figure 4 below):

Weakness, paralysis, numbness. Most CVA claimants are awarded disability benefits because of limitations in movement or motor ability, such as weakness and paralysis in an arm and leg on the same side of the body as a result of blockage (occlusion) in the middle cerebral artery or one of its branches.

Speech and language problems. Strokes sometimes produce some degree of loss of ability to understand or express certain aspects of written or spoken language in various combinations (known as aphasia).

Personality changes. A CVA far forward (anterior) in a frontal lobe might produce personality changes if it is large enough, without any physical limitations.

Vision problems. A CVA might involve the occipital lobes in the back of the brain. The occipital lobes process primary visual information and a stroke in that area would produce visual losses either in acuity (sharpness) or visual fields (how wide an area a person can see) without any other impairment. Major strokes that are not in the occipital lobes may result in visual field losses in the form of loss of half of the person’s visual field. Each half of the brain carries half the total visual information. Most CVAs only involve one side of the brain and therefore at the worst can only eliminate half of a person’s visual field in a pattern called homonymous hemianopsia0.

Balance problems. Strokes affecting the parietal lobes of the brain can produce distortions in the mental construction of space and cause loss of an awareness of body parts, a condition known as unilateral neglect. It is important that the neurological examination of a patient after a CVA detect unilateral neglect, because non-awareness of a limb makes it as functionally useless as paralysis. Strokes affecting the posterior circulation to the cerebellum can affect balance and ability to walk without producing any actual weakness.

Figure 4: The Circle of Willis, showing main cerebral arteries and the parts of the brain they supply.